Porphyromonas gingivalis, a gram-negative anaerobic, asaccharolytic bacterium is a recognized periodontal pathogen. It is cultured at elevated levels from advanced lesions of periodontitis and causes significant alveolar bone loss following experimental inoculation in nonhuman primates. P. gingivalis is highly proteolytic, degrading blood and connective tissue proteins (collagen, keratin, fibronectin, fibrinogen, immunoglobulin A, immunoglobulin G, plasma proteinase inhibitors, haptoglobin, hemopexin, and transferrin). Its ability to hemagglutinate erythrocytes is believed to be an early step in its abrogation of the immune response. I am using molecular approaches to study the virulent strains of P.gingivalis, and the components of my thesis project are: 1. Cloning and sequencing the hemagglutinin gene (hem). 2. Analyzing hem sequence data. 3. Determining percent DNA homology between strains. 4. Isolating unique, strain-specific random DNA clones. 5. Constructing a physical map of the chromosome. A paucity of genetic information about P. gingivalis is found in the literature, and fewer than a dozen of its genes have been cloned and sequenced to date. As genes are characterized, the physical map of the chromosome may provide critical information for other molecular microbiologists studying this and similar organisms.